Degradable oil tools have been developed which allow for temporary isolation of wellbores and which can be removed without intervention such as retrieval or drilling from the surface. These tools are generally fabricated from dissolvable or degradable metals or polymers, including degradable Al, Zn, and Mg alloys, and water-degradable polymers such as PVA, PLA and PGA. However, these degradable materials are not generally elastomeric, and non-degradable elastomeric seals are used to provide sealing against fluid flow.
Elastomeric sealing compounds that dissolve and degrade at rates similar to those of the degradable structural alloys (such as Tervalloy™), are stable for the period of operation under low temperatures during pumping operations, and degrade at high shut-in or flowback temperatures to reduce or eliminate any residual debris are desired. Such dissolvable, structural elastomeric materials are not readily available, and do not have the properties required or desired.
Biodegradable polymers and films have been developed that are formed from a water-dispersible polymer. For example, U.S. Pat. No. 6,296,914 (to Kerins et al.) describes a water-sensitive film that may include, for instance, polyethylene oxide, ethylene oxide-propylene oxide copolymers, polymethacrylic acid, polymethacrylic acid copolymers, polyvinyl alcohol, poly(2-ethyl oxazoline), polyvinyl methyl ether, polyvinyl pyrrolidone/vinyl acetate copolymers, methyl cellulose, ethyl cellulose, hydroxypropyl cellulose, hydroxypropyl methyl cellulose, ethyl hydroxyethyl cellulose, methyl ether starch, poly (n-isopropyl acrylamide), poly N-vinyl caprolactam, polyvinyl methyl oxazolidone, poly (2-isopropyl-2-oxazoline), poly (2,4-dimethyl-6-triazinyl ethylene), or a combination thereof. Some of these polymers, however, are not thermoplastic or moldable and, thus, are not readily processed using molding equipment. Further, these elastomers are also not elastic and, thus, may be limited in their use when considered for sealing applications.
In response to these and other problems with prior art elastomeric sealing compounds, attempts have been made to form water-shrinkable materials from elastomeric and water-dispersible polymers. One such elastomer is described in U.S. Pat. No. 5,641,562 to (Larson et al.). In one example, the elastomer contains polyethylene oxide having a molecular weight of about 200,000 and an ethylene vinyl acetate copolymer. Although such elastomers are shrinkable, they nevertheless are not dispersible or disintegrable in water so as to achieve complete flushability. Furthermore, the elastomers are not truly elastic.
A more recent elastomeric biodegradable film described in U.S. Pat. No. 8,338,508 (to Shi et al.) describes a water-sensitive film containing an olefinic elastomer that is both elastic and water-sensitive (e.g., water-soluble, water-dispersible, etc.) in that it loses its integrity over time in the presence of water. To achieve these dual attributes, the film contains an olefinic elastomer and a water-soluble polymer. Although these polymers are normally chemically incompatible due to their different polarities, Shi discloses that phase separation can be minimized by selectively controlling certain aspects of the elastomer, such as the nature of the polyolefin, water-soluble polymer, and other elastomer components, the relative amount of the elastomer components, and so forth. For example, certain water-soluble polymers that have a low molecular weight and viscosity can be selected to enhance their melt compatibility with nonpolar polyolefins. This, in turn, may result in a film that is generally free of separate phases, which would otherwise limit the ability of the water-soluble polymer to contact water and disperse. As such, Shi discloses the maintaining of the elastomeric and dissolvable components in a single phase, using chemistry developments to prevent segregation. These materials are suitable for use in the form of films, but do not have the structural properties required for high pressure sealing applications and cannot be fabricated into bulk objects.
In view of the current state of elastomeric materials, there is a need for an elastomeric material that dissolves and degrades at rates similar to those of the degradable structural alloys (such as Tervalloy™), which are stable for the period of operation under lower temperatures during pumping operations, and which degrades at high shut-in or flowback temperatures to reduce or eliminate any residual debris of the elastomeric materials in the wellbore.